Download Integumentary System

Collin County Community College
BIOL. 2401
(Chapter 5: pages 152 -170)
Integumentary System
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Definition
The integumentary system has 2 major components
 the cutaneous membrane
• epidermis
• dermis
SKIN
 accessory structures
• hair, nails
• multicellular exocrine glands
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Some
Skin
FactsSkin
Some
Facts
about
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A surface area of 1.5 - 2 square meters
Weighs approximately 4-5 kg (9-11 lbs.)
Every square centimeter contains:
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70 cm of blood vessels
55 cm of nerves
100 sweat glands
15 oil glands
230 sensory receptors
Half million cells that are constantly dying and being
replaced
Functions
• Protection of underlying tissues and organs
• Excretion of salts, water and organic wastes
• Maintenance of normal body temperature
• Storage of nutrients (fats)
• Detection of external stimuli
• Synthesis of Vitamin D3
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Skin Overview
The Epidermis
• Upper layer of the skin
• Consists out of an a-vascular stratified squamous
epithelium (nutrients need to diffuse from dermis up)
• The most abundant cells are Keratinocytes and they
form several strata
 thin skin has about 4 strata of cells
 thick skin has about 5 strata of cells
• These cells form karatin fibers that are at the basis of
protecting the top layer with a water resistant layer : the
stratum corneum
 stratum corneum is thicker in thick skin
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Thick vs Thin Skin
Epidermis layer sits on top of the Dermis ; they are
separated by the basal lamina - the basement
membrane to which the lower epidermal cells attach to.
Layers of Epidermis
In thick skin, 5 layers or strata can be identified.
Starting with the deepest stratum and moving
superficially, we recognize :
Stratum germinativum (basale)
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
In thin skin, the stratum lucidum is absent !
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Layers of Epidermis
Stratum basale or stratum germinativum
One cell layer thick and attaches to the basal lamina with
hemi-desmosomes and CAM’s
Large basal cells dominate which exhibit a high rate of
mitosis.
• Also contains melanocytes that produce the brown
pigment melanin
• Skin surfaces without hair also contain specialize
epithelial cell called Merkel cells; these are special
touch receptors.
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Stratum spinosum
• Contain the divided cells from the stratum basale,
which in turn divide themselves
• Typically 8 - 10 layers of cell thick
• Cells start to produce keratin
• Also contains Langerhans’ cells, which help in
stimulating a response to micro-organisms or
superficial skin cancers.
Stratum granulosum
•
Consists out of 3 -5 layers of cells
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Cells are actively producing keratin and keratohyalin,
which is visible by the granules in the cells.
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The cells are now far away from the closest blood
supply; they become flattened, organelles
disintegrate and they start to die off.
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Stratum corneum
• Located at the exposed area of the skin
• Depending on the thickness of the skin, it contains
several layers of dead , keratinized cells
• The cells are still connected via desmosomes, forming
a tight, water-resistant ( but not waterproof) cover
• This layer is important to prevent excessive water loss
from the interstitial fluid via the epidermis (called
insensible perspiration ~ 500 ml per day )
More Skin Facts
What happens to your skin when you soak in the bath tub too long ?
What happens to your skin when you soak in the sea too long ?
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Blisters
• Blisters are the result of
damage to the skin.
• Water accumulates in
pockets within the
epidermis.
• Simple blisters have water
pockets between
superficial and deeper
layers of epidermal cells.
• More severe blisters occur
when damage results in
water pockets between
dermis and epidermis !
Skin Color
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Three pigments contribute to skin color;
melanin, carotene, and hemoglobin
Melanin ranges in color from yellow to
reddish brown
Racial differences in skin coloring reflect
the relative kind and amount of melanin
Dark skinned people produce much more
and darker melanin than those of fair
skinned individuals
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Skin and Sunlight
• Sunlight stimulates melanocyte
to produce more melanin
• Melanin concentrates around
the nucleus and protects DNA
from UV radiation damage
• Freckles are an area of skin with
larger than normal production of
Melanin
Skin and Sunlight
• Sunlight also stimulates
karatinocytes to convert a
cholesterol derivative into Vitamin
D3 or Cholecalciferol
• Cholecalciferol is converted in the
liver and finally in the kidneys to
the hormone calcitriol.
• Calcitriol is an essential hormone
for absorption of calcium and
phosphate from the intestine
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The Dermis
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Located immediately deep to the epidermis
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This layer makes up the bulk of the skin
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A tough leathery layer composed of fibrous
connective tissue (areolar and dense irregular).
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Dermis is richly supplied with nerve endings,
blood vessels, and lymphatic vessels
The Dermis
The Dermis has two
regions
• Papillary region
• Reticular region
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Papillae and Epidermal Ridges
• Papillary region derived its
name from the dermal papillae
that extend into the epidermis
• The projections of the
epidermis into the dermis are
called the epidermal ridges
• Papillae and epidermal ridges
increase surface area of
contact and provide stronger
attachment of the layers
In thick skin, the surface of the skin follows
epidermal ridges, producing friction ridges which
are genetically determined ( e.g. fingerprints).
Reticular Region
• Papillary region contains small
capillaries and sensory neuron
endings embedded in areolar C.T.
• The Reticular region contains hair
follicles, sweat glands, larger blood
vessels, nerve fibers and sensory
organs.
• C.T is mostly dense irregular C.T.
with the collagen fibers extending
deeper into the hypodermis layer.
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Dermal Issues
• Skin is very flexible and allows for stretching
• Collagen fibers stop distortion when
stretching gets too bad
• Stretch-marks and wrinkles develop because
of damage to elastic and collagen fibers
• Collagen and elastic fibers run in bundles
• Orientation depends on stress the skin
experiences
• The pattern creates lines of cleavage
• Cuts parallel to lines of cleavage close
easier, heal faster and leave less scarring
SubCutaneous Layer
• Also called the HYPODERMIS
• Located immediately deep to the
Dermis layer
• NOT part of the skin but provides
important stabilization for skin and
underlying organs
• Superficial area contains many blood
vessels = subcutaneous plexus
• Rest contains mostly connective tissue
(areolar ) and fat tissue
• Subcutaneous injections
• Liposuction
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Accessory Structures
• Hair
• Exocrine glands
• Nails
Humans : the naked ape
• Humans have on
average 2.5 million
hairs
• 25 % are on the scalp
• Hair is produced in
hair follicles
Function
• Protect and insulate
the head
• Prevent unwanted
particles to enter nose,
eyes
• Provide extra
sensation to the skin
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Hair Structure
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The hair shaft projects from the skin
The root is embedded in the skin
The deep end of the follicle is
expanded and forms a hair bulb
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Central medulla
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Cortex surrounds medulla
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Flexible soft keratin
Layers of hard keratin
Cuticle on outside of cortex
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Most heavily keratinized
Hair Structure
• Hair growth starts in basal cells
near the center of the matrix
• They form medulla, cortex and
cuticle
• Hair is surrounded by dermal and
epidermal layers
• Internal root sheath : only
extends for a short distance
• External root sheath: reaches all
the way to the top of the skin
• Glassy membrane wrapped in a
thick outer connective tissue
sheath
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Hair Structure
Hair Accessories
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Arrector pili :
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Smooth muscle that causes hair to stand erect
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Contraction is result of fear, rage or response to
cold
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In hairy mammals this reflex helps as an insulation
barrier
Root hair plexus
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Sensory nerves that allow us to feel a single hair
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Skin Glands
• Sebaceous glands (oil glands).
• Eccrine sweat glands (merocrine).
• Apocrine sweat glands.
SEBACEOUS GLANDS
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Holocrine glands that Produce oily substance called sebum
Sebum lubricates the skin and has anti-bacterial properties
Most glands have ducts that empty into hair follicles.
Glands are very active right before birth. They stop after birth
but become activated again at puberty (acne).
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SWEAT OR SUDORIFEROUS GLANDS
• Eccrine sweat glands (merocrine).
• numerous and widely distributed
• palms and soles have highest numbers
• sweat contains 99% water; electolyte (NaCl),
organic components, antibiotics, waste products
• Functions to
•reduce body temperature ; FAILURE results in
heat stroke
•excrete some ingested drugs
•discourages bacterial growth
• Water loss via sweating is called sensible
perspiration (can be up to a gallon per hr)
SWEAT OR SUDORIFEROUS GLANDS
• Apocrine sweat glands.
• They are actually merocrine sweat glands
• produce odorous secretions since bacteria secretions
are nutrient source for bacteria
• secrete product into hair follicles
• located mostly in armpits, groin area
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SWEAT GLANDS
SWEAT GLANDS
Most Mammals
Humans
Few eccrine sweat glands
MANY eccrine sweat glands
Lots of apocrine glands
FEW of apocrine glands
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BRIEF OVERVIEW OF BURNS
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1st degree – damages only epidermis, a sunburn
with reddening of the skin
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2nd degree – burn destroys much of the epidermis
but leaves some epidermal remnants
– Re-growth from remnants is possible
– Blisters are common and pain is often severe
since the skin nerves are irritated by the
products of cellular destruction
BURNS
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3rd Degree – reaches to and through dermis –
often exposing muscle and bone
No epidermal remnants are present
No feeling because of destruction of nerves
Treatment requires skin grafts to provide
epidermal cells
Healing is slow at best
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BURN PROBLEMS
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Infection barrier is destroyed
Maintaining fluid
Maintaining electrolyte balance which requires
food and fluid intake
Contractures of skin and underlying CT and
muscle due to intense scarring
Thermoregulation problems
Skin Cancers
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The three major types of skin cancer are:
– Basal cell carcinoma
– Squamous cell carcinoma
– Melanoma
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Basal Cell Carcinoma
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Least malignant and most common skin cancer
Stratum basale cells proliferate and invade the
dermis and hypodermis
Slow growing and do not often metastasize
Can be cured by surgical excision in 99% of the
cases
Squamous Cell Carcinoma
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Arises from keratinocytes of stratum spinosum
Arise most often on scalp, ears, and lower lip
Grows rapidly and metastasizes if not removed
Prognosis is good if treated by radiation
therapy or removed surgically
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Melanoma
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Cancer of melanocytes is the most dangerous
type of skin cancer because it is:
– Highly metastatic
– Resistant to chemotherapy
Melanoma
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